Computer Assisted Surgery (CAS) systems are increasingly used for orthopedic operations in general, and for joint replacement surgeries in particular, in order to continue to improve the accuracy and long-term success of joint replacement surgery. The accuracy of cuts and drilled holes performed in joint replacement surgeries, such as in knee arthroplasty or total knee replacement (TKR) for example, is of prime importance, such that the installation of the implants can be made such that they best duplicate the kinematics of the natural knee.
Known optical, radio frequency and magnetic based CAS systems employ passive and active trackable elements affixed to objects, such as surgical tools and patient bone references, in order to permit the determination of position and orientation of the objects in three-dimensional space. Preoperatively taken images, computer generated models created from preoperative patient scans or intra operative landmark digitization are some of the methods used to provide accurate patient anatomical information to the CAS system, such that the real-time position of the same anatomical elements can be registered or calibrated and thus tracked by the CAS system, permitting these elements to be displayed to the surgeon in real time and their positions and orientations relative to the surgical tools used during the surgery.
Total knee replacement surgery, for example, typically requires one or more precise cuts to be made in the femur and/or tibia, such that the implant correctly fits and best replicates the geometry of a natural healthy knee. To perform these steps, in both conventional and CAS total knee replacement surgeries, it is known to use a tool or implement known as a surgical tool guide block which provides a drill and/or cutting guide to assist the surgeon when performing the steps required to prepare the femur and/or tibia for receiving the corresponding implant, including making a distal cut(s) in the femur.
Known TKR procedures include creating a distal cut in the femur such as to resect enough bone to permit the installation of the femoral implant. In conventional (i.e. non computer assisted) total knee replacement surgery, a distal cutting block is typically positioned and aligned by the surgeon and pinned in place on the anterior surface of the femur such that a cutting slot in the distal cutting block is aligned in the correct location for the distal cut. In CAS total knee replacement, it is also known to use a distal pin drill guide to accurately create pin holes in the distal end of the femur into which locating pins are inserted and employed to fix the distal cutting guide, either integrally formed with the distal pin drill guide or being a separate element, in the correct location to make the distal cut in the femur. Generally, the distal drill/cutting guide member comprises part of an assembly including an anterior guiding platform, that is fixed relative to the femur and on which the drill/cutting guide is displaceable by a selected, measurable amount to locate the drill/cutting guide in a desired position relative to the anterior guiding platform and therefore relative to the distal end of the femur. A tracked guide block is often intramedullarly fastened to the femur, and the anterior guiding platform can then be engaged thereto. Depending on the type of implant being used, and once aligned with the most distal femoral condyle, the drill/cutting guide can then be proximally displaced on the fixed anterior guiding platform by a selected amount corresponding to the amount of bone to be resected.
Therefore, the distally-mounted positioning block is fixed to the distal end of the femur using a bone screw or pins, and once the determined position for the cutting guide block has been established using this positioning block, the cutting block itself is then pinned directly in place on the bone, thereby requiring more drilled holes and additional pins inserted into the bone. The positioning block is typically then removed, leaving the cutting guide block pinned in place on the bone such as to be then able to make the necessary distal resection cut.
While this method has proven effective to date, there exits a need to reduce the invasiveness of TKR procedures such that less drilling, screwing and/or pinning directly into the bone, particularly on the distal end of the femur, is required.